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802.11 bandwidth
' Introduction' In wireless communication systems especially wifi system: every user can have equal access to use the network, and with the increasing demand for higher data rate, the requirement of improving wireless bandwidth is urgent for the network manager. The IEEE 802.11n standard gives users a better choice for using 40MHZ channel than 20MHZ channel that is called channel coding. With the increase of channel width the channel capacity also increased, so for high priority users, this can help to maintain their bandwidth. 20MHZ channel's Problems and solutions: Problem1: traditional 20MHZ system can no longer meet the need of high data rate and broad bandwidth. In 2.4GHZ system it only contains three 20MHZ channels. Solution1: '''5GHZ 40MHZ system. ]] As the use of 802.11n two 20MHZ channel can be combined into one 40MHZ channel then the bandwidth increased significantly, and with 5GHZ frequency, there are more channels can be take into use, due to the higher channel frequency. Different modulation scheme will lead to different data rate, and theoretically with channel bonding the data rate can be doubled. From the table in the left side, it can be easily find out that theoretical data rate of of 40MHZ is more than double the rate of 20MHZ under the same modulation scheme. This provides us a great opportunity to increase the channel bandwidth. In figure.1 it shows the data rate of 20MHZ system and 40MHZ system in a real situation. It can be found that the data rate of 40GHZ system is always higher than 20MHZ system, but not as much as double the rate of 20MHZ, this is due to the severe interference. Because higher frequency means smaller interval between different channels, so it is much more easier to give rise to the interference between different channel. And another thing can be noticed is that if the distance between transmitter and receiver is very large, the advantage of 40MHZ will disappear. The cause of the problem is that for a higher carrier frequency calls for higher transmission power to maintain the transmission range, if the power is same, the range of 40MHZ system will be smaller than 20MHZ system. '''Problem2: '''Although higher frequency leads to not only more channels but also severe interference and smaller coverage area. In traditional SISO(single input single output ) system this problem can not be eliminate. '''Solution2: With the ideal of MIMO(multiple input and multiple output ) being proposed, this problem can be mitigated. MIMO systems in IEEE 802.11n promise new potential for channel bonding and higher transmission rates. MIMO use multiple transmit antennas to transmit multiple data stream simultaneously along the same channel2. Taking the advantage of spatial diversity and spatial multiplexing, MIMO can use of the multiplicity of data streams to improve SNR and average throughput at the same position, then transmits the same signal over different antennas at the same time, while spatial multiplexing. Conclusion: Comparing with traditional 2.4GHZ 20MHZ system, 5GHZ 40MHZ system provides broader bandwidth and higher data rate with the help of MIMO scheme. But it requires higher transmission power to maintain the coverage. Reference List: 1 Venkat Ramana, P., & Narayana Reddy, S. (2012, March). Improved performance of UDP & TCP throughput in Wi-Fi networks for voice and data services in mobile communications with MIMO systems. In Devices, Circuits and Systems (ICDCS), 2012 International Conference on (pp. 144-148). IEEE. 2Deek, L., Garcia-Villegas, E., Belding, E., Lee, S. J., & Almeroth, K. (2011, December). The impact of channel bonding on 802.11 n network management. In Proceedings of the Seventh COnference on emerging Networking EXperiments and Technologies (p. 11). ACM.